The LORD is King for ever and ever: the heathen are perished out of his land.
The third part and third strophe.
The Lord is King for ever and ever. Sense had suggested the thought, that because of the prevailing might and impunity of oppressors, the Lord has ceased to reign on His high throne as righteous Governor, Judge and King over the earth, especially in relation to His people (Deuteronomy 33:5; Numbers 23:21). Faith now shows David how impotent are the rebels' efforts to set up in opposition a kingdom of unrighteousness. Yahweh is, and ever will abide, "King" alone.
The pagan are perished - all who, whether nominally of the elect nation or not, are paganish in heart and life (Ezekiel 16:3; Jeremiah 9:25; Psalms 9:19). What was a prayer in Psalms 9:19, "Let the pagan be judged," is here taken as an accomplished fact in the confidence of faith, "the pagan are perished."
Out of his land - implying why the pagan are perished out of the land (first, Canaan; then, ultimately, the whole earth) - namely, because the land is not theirs, but YAHWEH'S!